This invention relates to a highly lubricative sound-absorbing material and a cable reel including the same, and more particularly it relates to a highly lubricative sound-absorbing material preferably adapted to be used in a cable reel which is mounted on a steering device for an automotive vehicle and electrically interconnects a stationary element assembly and a movable element assembly through a flat cable.
In an automotive vehicle equipped with an air bag, a cable reel is provided in a steering wheel in order to supply electrical power to an air bag system. For convenience of explanation, such a cable reel will be described below by referring to the drawings. FIG. 5 is a schematic longitudinal sectional view of a conventional cable reel. FIG. 6 is a perspective view of a conventional sound-absorbing material. As shown in FIG. 5, the conventional cable reel includes a movable element assembly, which rotates together with a steering wheel and a stationary element assembly 2 which is secured to a stationary shaft on a body frame. The movable and stationary element assemblies 1 and 2 define an annular cable containing chamber 3 which accommodates a flat cable 4 in a swirl manner. Opposite ends of the flat cable 4 in the swirl manner connected to lead wires 6 and 7 which are led out from the movable and stationary element assemblies 1 and 2, respectively, to be connected to an external connector or electrical wires. In such a cable reel, the flat cable 4 is wound in the cable containing chamber 3 when the steering wheel is turned in either a clockwise or counter-clockwise direction while the flat cable 4 is unwound in the chamber 3 when the steering wheel is turned in the other direction, so that a device (air bag) on the steering wheel is electrically connected to a power source on the body frame.
The cable reel involves a problem of unpleasant sliding noise caused when the lateral opposite edges of the flat cable 4 slide on upper and lower bearing walls of the cable containing chamber 3 upon winding and unwinding of the flat cable 4 in the chamber 3. The flat cable 4 caused to vibrate in an axial direction (from upper to lower direction or from lower to upper direction) A of the steering wheel during idling or driving of the automotive vehicle, thereby causing a problem of unpleasant vibration noise due to collision between the bearing surfaces of the chamber 3 and the lateral opposite edges of the flat cable 4.
Japanese Utility Model Publication No. HEI 6-36040 (1994) discloses a cable reel in which a highly lubricative sheet such as an polytetrafluoroethylene resin or the like is adhered to at least one of bearing surfaces of a cable containing chamber in order to attenuate sliding noise. Also, Japanese Patent Public Disclosure No. HEI 8-104471 (1996) discloses a cable reel in which a sound-absorbing material 5 made of a resilient material such as a rubber or the like or a sound-absorbing material 5 with the poly-tetrafluoroethylene resin is attached to bearing surfaces of stationary and movable element assemblies by means of clamps provided on the surfaces (see FIG. 5).
The polytetrafluoroethylene resin is adhered by way of PET (polyethylene terephthalate) to a surface of a rubber sheet since the former lacks adhesion to the latter.
Although the polytetrafluoroethylene resin sheet disclosed in Japanese Utility Model Publication No. HEI 1-36040 (1994) can attenuate the sliding noise on account of its high lubrication, it cannot reduce noise which is caused by collision of the flat cable onto the bearing surfaces of the cable reel due to axial vibrations of the cable in swirl. In particular, such unpleasant collision noise are likely to be pronounced when an engine is idling. On the other hand, the resilient sheet disclosed in Japanese Patent Publication No. HEI 8-104471 (1996) hardly attenuates sliding noise, since the lubrication between the flat cable and the resilient sheet is poor, although the sheet can reduce the collision or vibration noise.
A rubber sheet having the polytetrafluoroethylene resin provided thereon can attenuate both sliding noise and vibration noise by means of the highly lubricative resin and rubber sheet.
However, as shown in FIG. 6, a rubber sheet 5a, a PET film 5b, and an polytetrafluoroethylene resin sheet 5c must be punched out into an annular shape adapted to be used, since the bearing surfaces of the cable containing chamber is in an annular form. Consequently, this involves much loss of material. In particular, a total cost of the cable reel becomes high since the polytetrafluoroethylene resin sheet is expensive.
In addition, the above lubricative sound-absorbing material involves a high producing cost due to increase of working steps, since the PET film is adhered to the rubber sheet through an adhesive and then the ethylene tetrafluoride resin is adhered to the PET film by way of an adhesive.
Further, the above lubricative sound-absorbing material gives rise a problem in that it reduces a sound-absorbing effect since the hard PET film is interposed between the rubber sheet having a sound-absorbing function and the polytetrafluoroethylene resin having a lubricative function. It is difficult to produce an ethylene tetrafluoride resin sheet having a low thickness since it is produced by means of skiving. Consequently, the sheet on the market is usually more than 20 .mu.m. Such a thick polytetrafluoroethylene resin sheet in addition to the hard PET film will lower the sound-absorbing function.